1. Field of the Invention
The present invention relates to a polymer scale preventive agent and a polymerization vessel for use in polymerization of a monomer comprising a haloethylene, and a process for preparation of a haloethylene polymer using the vessel.
2. Description of Prior Art
In processes of preparation of polymers by polymerizing a monomer in a polymerization vessel, the problem that polymers deposit on the inner wall surface and other parts which come into contact with the monomer such as stirring blades of the polymerization vessel in the form of scale, is known. The deposition of the polymer scale on the inner wall results in disadvantages that the yield of the polymer and the cooling capacity of the polymerization vessel are lowered; that the polymer scale may peel and mix into manufactured polymer, thereby impairing the quality of the manufactured polymer; and that removal of such polymer scale is laborious and hence time-consuming. Further, since the polymer scale contains unreacted monomers, there is a danger that the operators may be exposed to the unreacted monomers, which may cause some physical disorders.
Heretofore, there are known methods for preventing polymer scale deposition in which the inner wall and so forth are coated with a suitable substance as a polymer scale preventive agent.
Such substances suited as polymer preventive agents include, for example, particular polar compounds (Japanese Patent Publication (KOKOKU) No.45-30343(1970)); dyes or pigments (Japanese Patent Publication (KOKOKU) Nos. 45-30835(1970)) and 52-24953(1977)); aromatic amine compound (Japanese Pre-examination Patent Publication (KOKAI) No. 51-50887(1976)); a reaction product of a phenolic compound with an aromatic aldehyde (Japanese Pre-examination Publication (KOKAI) No. 55-54317(1980)).
However, it is not necessarily to attain satisfactory prevention of scale deposition in the polymerization or copolymerization of a monomer having an ethylchic double bond comprising a haloethylene such as a vinyl halide, a vinylidene halide or the like as an essential component.
Where polymerization is repeated in the same polymerization vessel internally coated with a conventional polymer scale preventive agent, the scale preventing effect will gradually be lowered. Specifically, if scale deposition cannot be recognized by naked eyes after a polymerization run, a thin layer of scale may have been formed actually. Once such a thin layer has been formed, even if a coating of a scale preventive agent is formed before each batch of polymerization, the coating may peel and mix into the polymerization liquid. This reduces the number of polymerization runs in which deposition of polymer scale is effectively prevented, resulting in that far from improving productivity, it impairs the quality of polymeric products.
Further, in the polymerization of a haloethylene or the copolymerization of a monomer mixture containing largely a haloethylene, the effect of preventing polymer scale deposition varies depending on the kinds of additives, e.g., a polymerization initiator, a chain transfer agent, a suspension agent, etc., the type of polymerization, and materials constituting the inner wall of polymerization vessels. Therefore, the development of a more excellent polymer scale preventive agent whose performance is not affected by any polymerization conditions is desired.